Unknown Edge in Ipad after applying Subsurf Modifier
There are a few interiror faces in the frame of the device (marked on the first picture) which cause this problem. You used the same face for the backplate of the ipad and for the screen what is never recommended, create two independent face for them.

After you fixed the geometry you have to add mean crease to the sharp edges (marked on the second picture).

After you apply the modifier the best if you dissolve the middle edges to avoid the unnecessary bending (third picture).

https://blend-exchange.giantcowfilms.com/b/odmEMaaY